Smoke detector having variable level sensitivity

ABSTRACT

A smoke detector having variable sensitivity to smoke levels and using one button both to test the smoke detector and actuate a mode of diminished sensitivity to smoke levels. The smoke detector is operable in a normal sensitivity mode and a diminished sensitivity mode with rapid switching between the modes. The sensitivity to smoke levels is substantially constant when in either the normal or diminished sensitivity mode.

The present invention relates generally to a smoke detector having theability to temporarily change its sensitivity to smoke levels. Moreparticularly, the invention is concerned with a smoke detector.[.have.]. .Iadd.having .Iaddend.a single button to test the smokedetector and also to activate a temporary period of diminishedsensitivity to smoke levels. The change from diminished sensitivity tonormal sensitivity operation is also characterized by a rapid switchingfrom one smoke sensitivity level to the other.

Various smoke detectors include the ability to operate for a short timein a silent mode during which the smoke detector is rendered inoperativein order to avoid false alarms associated with smoke from cooking orfrom persons smoking. Other units are not rendered totally inoperativebut have a rapidly changing level of smoke sensitivity over a temporaryperiod of diminished smoke level sensitivity. Furthermore, current smokedetectors having these features do not allow testing of the operabilityof the smoke detector during the silent period, and currently availablesmoke detectors generate an unpleasant beeping sound during the silentoperational mode. Also, such smoke detectors have different buttons totest the unit and to actuate the silent mode of operation. Such unitshave substantial disadvantages to the user including, (a) the user canmistakenly push the test button generating an alarm signal (b) the usercan inadvertently push the test button of a failed smoke detectorcausing the user to falsely believe the silent mode has been activated,(c) the user can even be confused as to the function of each of the twobuttons, or (d) the user can inadvertantly push the silence button of asmoke detector, not get a response, and then push the test button andadditionally not get a response since the unit been previously silenced,which can substantially confuse the user and make him think the detectorhas failed.

BRIEF SUMMARY OF THE INVENTION

One of the primary objects of the invention is to provide an improvedsmoke detector having a single button for both testing .[.operabiilty.]..Iadd.operability .Iaddend.of the smoke detector and also for actuatingan operational mode of diminished sensitivity to smoke levels.

It is another object of the invention to provide a novel smoke detectorhaving a single button for both actuating a mode of diminished smokelevel sensitivity and for testing the smoke detector while overridingthe diminished sensitivity mode during the testing mode.

It is further object of the invention to provide a novel smoke detectoroperable in a mode of normal sensitivity to smoke levels and in a modeof diminished sensitivity to smoke levels, the sensitivity remainingsubstantially constant throughout at least a majority of the time periodin the diminished sensitivity mode.

It is an additional object of the invention to provide a novel smokedetector operable for a temporary time period in a mode of diminishedsensitivity to smoke levels and at the end of the temporary time periodthe detector switches rapidly to the normal mode of operation.

It is an object of the invention to provide an improved smoke detectoroperable for a temporary time period in a mode of diminished sensitivityto smoke levels with the smoke alarm remaining quiet unless the smokelevel exceeds an increased predetermined smoke level.

A feature of the smoke detector in accordance with the invention lies inthe provision of a single user button or switch for controlling bothtesting of the smoke detector and for actuating a mode of temporarilydiminished sensitivity to smoke levels. Testing of the smoke detectorcan be performed at all times, overriding if necessary the mode ofdiminished sensitivity to smoke levels. During this mode of diminishedsensitivity the smoke detector still acts to sense and provide an alarmfor the presence of smoke levels exceeding a predetermined smoke levelwhich is increased over the normal mode alarm smoke level.

During the mode of diminshed sensitivity to smoke levels, the preciseamount of smoke level sensitivity is maintained constant over at least amajority of the temporary time period during which the diminishedsensitivity mode is operative. At the end of the temporary time periodthe smoke detector switches rapidly back to the normal sensitivity modeof operation.

Further objects and advantages of the present invention, together withthe organization and manner of operation thereof, will become apparentfrom the following detailed description of the invention which taken inconjunction with the accompanying drawings wherein like referencenumerals designate like elements throughout the several views.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a smoke detector constructed in accordancewith one embodiment of the invention;

FIG. 2 is an electrical circuit diagram of one form of the invention;

FIG. 3 shows a control signal plotted as a function of time illustratingthe signal level of the sensitivity control element during the normalsmoke detector mode and during the temporary period of diminishedsensitivity smoke level;

FIG. 4 illustrates voltage on the collector plate versus smokeobscuration percentage; and

FIG. 5 shows sensitivity level of a transistor during both normal anddiminished sensitivity modes of operation.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring now to the drawings and in particular to FIGS. 1 and 2, asmoke detector constructed in accordance with one embodiment of thepresent invention is indicated generally at 10. The smoke detector 10includes a single element, such as a switch 12, which can be used tointeract with the smoke detector 10 by user actuation of the switch 12.The switch 12 is moved along the direction of arrow 13 into contact witha container 14 defining an ionization chamber 16. The ionization chamber16 is one .[.exampe.]. .Iadd.example .Iaddend.of means for sensing smokelevels and is a conventional unit having an Americium isotope source 17(Am²⁴¹) supplied by Nuclear Radiation Development, Buffalo, N.Y. Theisotope source 17 emits alpha particles designated as 18, and theionization chamber 16 is vented to admit smoke. The alpha particles 18ionize the atmosphere in the ionization chamber 16 in a known manner,providing a conductive path between the container 14 and the isotopesource 17. The voltage at collector plate 20 is potentiometricallydivided between the voltage at the container 14 and the isotope source17. It is a design convenience that the isotope source 17 also functionsas one conductive terminal of the ionization chamber 16. Theintroduction of smoke into the ionization chamber 16 causes the voltageat the collector plate 20 to change in a known manner (see FIG. 4) suchthat the voltage is a function of the smoke .[.levels.]. .Iadd.level.Iaddend.in the ionization chamber 16. In FIG. 4 the photocell used formeasuring the smoke obscuration level (as required by UnderwritersLaboratory Standard 217) is manufactured by Weston Instruments, ModelNo. 594R.R. Another example of conventional sensing means is aphotoelectric sensor system.

When the user wishes to test the operability of the smoke detector 10,the user moves the switch 12 into contact with the container 14; andapproximately 90 microamps current flows from a battery 22 having inputterminal 24. This current flows through resistor 25 in parallel with.[.a resistor 26 and.]. the base-emitter (B-E) junction of a transistor27 .Iadd.and into resistor 26. .Iaddend.About seventy-two micro amps ofcurrent flows into the base-emitter (B-E) junction of the transistor 27which induces a current in the collector (C) of the transistor 27. Theresistors 25 and 26 and the transistor 27 shown in FIG. 2 form a testswitch sensor 28 illustrated in FIG. 1. Once the transistor 27 is turnedon, the current source generated at the transistor 27 is approximatelytwenty to forty milliamps, this current being dependent on thetransistor 27 DC beta, or current gain. Acting as a current source, thetransistor 27 charges a capacitor 30 through a diode 32 andsubstantially simultaneously turns on a second transistor 34 through aresistor 36. The capacitor 30, a resistor 38 and a resistor 40 in FIG. 2form a time constant circuit 42 in FIG. 1, and this circuit 42 will bediscussed in more detail hereinafter as part of our explanation of thediminished sensitivity operational mode.

During the mode of testing the operability of the smoke detector 10, aninhibiting means, such as an inhibit control circuit 44 shown in FIG. 1,is used for inhibiting actuation of the mode of .[.dimished.]..Iadd.diminished .Iaddend.sensitivity to smoke levels. Components of theinhibit control circuit 44 include the resistor 36, a resistor 46 andthe transistor 34 shown in FIG. 2. The inhibit control circuit 44prevents the time constant circuit 42 from activating and controllingoperation of the diminished sensitivity mode. In the illustratedembodiment a Darlington transistor 48 (such as, for example, a MPSA12,NPN transistor) acts as a control switch 50 (see FIG. 1) for activationof the diminished sensitivity mode. The control switch 50 functions todetermine the current flow to a transistor 56, and along with coupledresistors, acts as a sensitivity control 58 during the .[.diminishd.]..Iadd.diminished .Iaddend.sensitivity operational mode (to be discussedin detail hereinafter).

During operation of the inhibit control circuit 44, the transistor 34saturates via the current flow through the resistor 36 and pulls thebase B of the transistor 48 to about 100 millivolts. This prevents thetransistor 48 from turning on and the emitter E of the transistor 56floats at a voltage relative to the circuitry. Pin numbered P13 of asmoke detector chip 60 with a voltage comparator portion (such as, aMotorola MC14467-P1) settles to fifty percent of the battery voltage (9VDC in the illustrated embodiment), or 4.5 VDC at the pin P13. Thevoltage comparator portion of the chip 60 compares the 4.5 VC at the pinP13 with the voltage at pin P15, which is the input from the ionizationchamber collector plate 20. During the testing mode when the switch 12contacts the container 14, a circuit to ground 62 is completed boththrough a resistor 64 and to a ground 66 through the container 14. Thesecomplete circuits therfore form a voltage divider network with a voltageon the container 14 of about 6.08 VDC, and thus a voltage ofapproximately four VDC at the collector plate 20. This voltage isdependent on the manufacturer's calibration of the ionization chamber16. Consequently, in the test mode the 4.0 VDC input from the collectorplate 20 to the pin P15 is less than the voltage of 4.5 VDC at the pinP13. This difference in voltage results in the voltage comparatorportion of the chip 60 outputting an alarm signal on pin P10 and P11, inconjunction with P8, and also with P5 (LED) to alarm generating means,such as a conventional light emitting diode 61 and a.[.pieozoelectric.]. .Iadd.piezoelectric .Iaddend.horn 68. The horn 68includes a pieozoelectric ceramic disk (not shown), such as a KyoceraNo. KBS-350A-3FCS-2 , manufactured by Kyocera, Ltd., Japan. The ceramicdisk is mounted in a transducer socket, such as an ATM 7373,manufactured by Molex, Inc., Lisle, Ill. The transducer socket (notshown) provides an audio output in coordination with the.[.piezolectric.]. .Iadd.piezoelectric .Iaddend.disk. In the preferredembodiment this push-to-test operational mode always overrides any othermode of operation, including the normal operating mode and the mode ofdiminished sensitivity to smoke levels.

In the illustrated embodiment as long as the user maintains the switch12 in a depressed position in contact with the container 14, the inhibitcontrol circuit 44 is operative, thereby preventing the time constantcircuit 42 from controlling the diminished sensitivity mode. Once theuser releases the switch 12, current is no longer supplied through thecollector C of the transistor 27 to the inhibit control circuit 44. Thetransistor 34 is also shut off, the time constant circuit 42 now turnson the transistor 48, and the mode of diminished .[.snesitivity.]..Iadd.sensitivity .Iaddend.to smoke levels becomes operative. In otherforms of the invention the diminished sensitivity mode can be actuatedindependently of the testing mode while still using only one button orswitch. This could be accomplished, for example, by a simple timingcircuit such that a momentary depression of the switch 12 actuates thediminished sensitivity mode but requires a substantially longer contacttime to enter the test mode. In the illustrated embodiment the timeconstant circuit 42 sets a time period of about thirteen minutes foroperation of the diminished sensitivity mode. The time constant circuit42 supplies a current to the base B of the transistor 48. Preferably,the capacitor 30 of the time constant circuit 42 is a high quality,.[.low-leakge.]. .Iadd.low-leakage .Iaddend.electrolytic capacitor whichassures an accurate time period when using high resistance values forthe resistors 38 and 40 of the time constant circuit 42. Duringoperation of the time constant circuit 42, the diode 32 blocks thedischarge to ground of the capacitor 30 back through the resistors 36and 46 and through the transistors 34.

Once the time constant circuit 42 is actuated, approximately 0.9microamps initially flows into the base--emitter (B-E) junction of thetransistor 48,causing .[.its saturation with.]. .Iadd.it to saturatewith current supplied by .Iaddend.the components connected to thecollector C, such as resistors 70 and 72 and the transistor 56. Asindicated hereinbefore, the transistor 48 is also the control switch 50(see FIG. 1) which outputs a control signal via its saturation tocontrol current flow to the transistor 56 (also the sensitivity control58). When the transistor 48 is conducting, the transistor 56 acts as anemitter--follower based on the voltage divider ratio established by theresistors 70 and 72. In the .[.emobodiment.]. .Iadd.embodiment.Iaddend.of FIG. 2, the voltage divider ratio is such that thetransistor 48 saturates at about 0.5 VDC, causing a potential of about2.5 VDC to be placed at the base B of the transistor 56. This locks theemitter E of the transistor 56 at 3.0 VDC when the internal voltagesetting resistance ladder and voltage comparator of the chip 60 isstrobed on. This resistance ladder has a large impedance (about 1megaohm) which appears as a current source to the transistor 56, andthus the .[.resistance ladder.]. .Iadd.transistor 56 .Iaddend.easilyclamps the input pin P13 of the voltage comparator portion of the chip60 to about 3.0 VDC (roughly 1/3 the voltage of the battery 22). Whenthe control switch 48 is not on, the emitter E of the transistor 56floats; and the voltage at pin P13 returns to about half of the voltageof the battery 22 when the chip 60 strobes on. This voltage level of 3.0VDC for the pin P13 corresponds to about a three percent smokeobscuration level in the ionization chamber 16 for the followingconditions; the buffered .[.collection plate.]. .Iadd.collector plate 20.Iaddend.voltage is plotted against smoke obscuration level in a smokebox (see FIG. 4) with approximately thirty-four feet per minute airflow, and the initial voltage of the collector plate 20 is set to about5.74 VDC. During normal sensitivity operation a predetermined smokelevel for alarm signal generation is about one and a half percent smokeobscuration (also known as optical smoke density) .Iadd.which isconventionally defined in % obscuration per foot.Iaddend.. During themode of diminshed sensitivity to smoke levels, an alarm signal will begenerated if the smoke level in the ionization chamber 16 exceeds theincreased predetermined smoke level of three percent obscuration,corresponding to changing the voltage on the collector plate 20 to lessthan 3.0 VDC. This smoke signal is input to pin P15 of the voltagecomparator portion of the chip 60 and compared with the voltage pin P13.This setting is for light to moderate smoke levels and suppresses alarmsassociated with various user generated conditions, such as, for example,at least one of cooking smoke, fireplace smoke, excessive water vaporfrom bath facilities and from persons smoking cigarettes, cigars orpipes. In another form of the invention the user can select differentsensitivity levels through the sensitivity control 58 which can includeselectable different ones of the transistors 56 or resistors, such asthe resistors 70 and 72.

At the end of the thirteen minute time period, dictated by the timeconstant circuit 42, the capacitor 30 has discharged sufficiently tocause the transistor 48 to turn off. The base junction B of thetransistor 56 is then pulled positive to the supply. The changeover fromthe diminished sensitivity to the normal sensitivity smoke detector modeoccurs rapidly as illustrated in FIG. 3. In this figure the voltage atthe collector C of the transistor 48 is the control signal. The voltagebehavior in FIG. 3 does give a relative measure of the behavior of thesensitivity and is plotted over a small part of the normal mode and overthe temporary time period of the diminished sensitivity mode. At the endof this temporary time period the voltage for the transistor, 48 shows arapid decay, or a change from saturation to cut-off. This rapid decayarises from the use of an .[.appropirate.]. .Iadd.appropriate.Iaddend.diminishing means, which in the illustrated embodiment isamplifying means, such as the transistor 48, and comprises the operatingfeature of having a small current input, a large gain and a .[.smallgain.]. .Iadd.small current .Iaddend.output. As noted in a relativemanner in FIG. 3 the resulting control signal level has a substantiallyconstant magnitude over at least a majority of the temporary time periodof operation in the diminished sensitivity mode; and this in .[.turns.]..Iadd.turn .Iaddend.provides a substantially constant level ofdiminished sensitivity to smoke levels over the temporary time period.This aspect is illustrated in more quantitative and absolute terms inFIG. 5 which plots the emitter (E) voltage of the transistor 56 over thetemporary time period. The change of sensitivity levels is clearly shownas one proceeds from the normal mode at 4.5 VDC to about three voltsduring the diminished sensitivity mode. This feature of the inventionyields a highly reliable smoke sensitivity in the .[.dminished.]..Iadd.diminished .Iaddend.sensitivity mode and also exhibits a rapidchangeover to normal smoke sensitivity levels. At any time the temporaryperiod of diminished sensitivity can be reinstituted by the user againdepressing and releasing the switch 12 to start the thirteen minutetemporary time period.

Therefore, in accordance with the present invention a smoke detector isprovided which includes a number of features having important commercialadvantages. A user actuated switch controls both testing of the smokedetector and engagement of an operational mode of diminished sensitivityto smoke levels. The user can override any other operational mode andperform testing of the smoke detector. Once the smoke detector is in thediminished sensitivity mode, the sensitivity to smoke levels issubstantially constant over the temporary time period of diminished modeoperation, providing a highly reliable smoke detection sensitivity whiletolerating user generated conditions, such as cooking smoke or cigarettesmoke. At the end of the temporary time period there is a rapidswitching back to the normal sensitivity mode of sensing smoke levels.

While preferred embodiments of the present invention have beenillustrated and described, it will be understood that changes andmodifications may be made therein without departing from the inventionin its broader aspects. For example, the invention has been illustratedin terms of a collection of discrete components, but it is contemplatedthat the circuitry can be readily embodied within an integrated circuitchip. Various features of the invention are defined in the followingclaims.

What is claimed is:
 1. A smoke detector comprising:means for sensingsmoke levels and generating a signal .[.charcteristic.]..Iadd.characteristic .Iaddend.of said smoke levels; means for generatingan alarm signal responsive to said sensing means detecting apredetermined smoke level; means for user testing the operability ofsaid smoke detector, said testing means comprising a single user.[.actuaed.]. .Iadd.actuated .Iaddend.element adapted to causegeneration of said alarm signal; and means for temporarily diminishingthe sensitivity of said smoke detector by increasing in said sensingmeans the magnitude of said predetermined smoke level causing generationof said alarm signal, said single user element further adapted toactuate said diminishing means.
 2. The smoke detector as defined inclaim 1 wherein said sensing means comprises at least one of anionization chamber/radioactive source and a photoelectric sensor system.3. A smoke detector comprising:means for sensing smoke levels andgenerating a signal characteristic of said smoke levels; means forgenerating an alarm signal responsive to said sensing means detecting apredetermined smoke level; means for testing the operability of saidsmoke detector, said testing means comprising a user actuated elementadapted to cause generation of said alarm signal; and means fortemporarily diminishing the sensitivity of said smoke detector byincreasing in said sensing means said predetermined smoke level causinggeneration of said alarm signal, said user actuated element furtheradapted to actuate said diminishing means and said user testing meansoverriding the operation of said diminishing means during the operationof said testing means.
 4. A smoke detector comprising:means for sensingsmoke levels and generating a signal .[.charcteristic.]..Iadd.characteristic .Iaddend.of said smoke levels; means for generatingan alarm signal responsive to said sensing means detecting apredetermined smoke level; means for user testing the operability ofsaid smoke detector, said testing means operable by the user forgenerating an alarm signal output to said alarm signal means; and meansfor diminishing for a temporary time period the sensitivity of saidsmoke detector by increasing in said sensing means the magnitude of saidpredetermined smoke level causing generation of said alarm signal, saiddiminishing means generating a control signal for establishing theincreased magnitude of said predetermined smoke level, and said controlsignal having a substantially constant magnitude during said temporarytime period.
 5. A smoke detector comprising:means for sensing smokelevels and generating a signal .[.charcteristic.]. .Iadd.characteristic.Iaddend.of said smoke levels; means for generating an alarm signalresponsive to said sensing means detecting a predetermined smoke level;means for user testing the operability of said smoke detector, saidtesting means operably by the user for generating an alarm signal outputto said alarm signal means; and means for diminishing for a temporarytime period the sensitivity of said smoke detector by increasing in saidsensing means the magnitude of said predetermined smoke level causinggeneration of said alarm signal, said diminishing means generating acontrol signal over said temporary time period and said control signalhaving a slowly changing level until the end of said temporary timeperiod whereupon said control signal decays rapidly causing deactivationof said diminishing means.
 6. The smoke detector as defined in claim 5wherein said diminishing means comprises at least means for amplifying asmall current input and having a large gain and small current output. 7.The smoke detector as defined in claim 5 wherein said increasedpredetermined smoke sensitivity level comprises a moderate smoke levelassociated with user generated conditions.
 8. The smoke detector asdefined in claim 7 wherein said user generated conditions comprise atleast one of cooking smoke, fireplace smoke, excessive water vapor andpersons smoking cigarettes, cigars or pipes.
 9. A smoke detectorcomprising: means for sensing smoke levels and generating a signal.[.charcteristic.]. .Iadd.characteristic .Iaddend.of said smokelevels;means for generating an alarm signal responsive to said sensingmeans detecting a predetermined smoke level; means for user testing theoperability of said smoke detector, said testing means comprising a useractuated element adapted to cause generation of said alarm signal; meansfor diminishing for a temporary time period the sensitivity of saidsmoke detector by increasing in said sensing means said predeterminedsmoke sensitivity level causing generation of said alarm signal, saiduser element being a single element and adapted to both actuate saiddiminishing means and operate said testing means; and sensitivitycontrol means for user selection of said increased predetermined smokelevel.
 10. The smoke detector as defined in claim 9 wherein said alarmsignal means comprises a voltage comparator.
 11. The smoke detector asdefined in claim 10 further including alarm generating means.
 12. Thesmoke detector as defined in claim 11 wherein said alarm generatingmeans comprises a horn and light emitting diode.
 13. The apparatus asdefined in claim 1 wherein said alarm signal means remains quiet unlessuser tested or said smoke levels exceed said increased predeterminedsmoke level during operation of said diminishing means or said smokelevels exceed said predetermined smoke level during the normal operationof said smoke detector.
 14. The apparatus as defined in claim 1 furtherincluding means for inhibiting operation of said diminishing means for auser selected time period.
 15. A smoke detector comprising:means forsensing smoke levels; means for generating an alarm signal responsive tosaid sensing means detecting a predetermined smoke level; means for usertesting the operability of said smoke detector, said testing meanscomprising a user actuated element adapted to cause generation of saidalarm signal; and means for temporarily diminishing the sensitivity ofsaid smoke detector by increasing in said sensing means saidpredetermined smoke level causing generation of said alarm signal, saiduser testing means overriding the operation of said diminishing meansduring the operation of said testing means.
 16. A smoke detector havinga normal sensitivity level and a moderate sensitivity level,comprising:means for sensing smoke levels and generating a signalcharacteristic of said smoke levels; means for generating an alarmsignal responsive to said sensing means detecting a predetermined smokelevel; means for user testing the operability of said smoke detector,said testing means operably by the user for generating an alarm signaloutput to said alarm signal means; and means for diminishing for atemporary time period the sensitivity of said smoke detector to saidmoderate sensitivity level for activating said alarm signal, and said.[.dminishing.]. .Iadd.diminishing .Iaddend.means generating a controlsignal having a slowly changing magnitude during said temporary timeperiod and a rapidly changing magnitude at the end of said temporarytime period, whereupon the sensitivity of said smoke detector returns tosaid normal level.
 17. A smoke detector comprising:means for sensingsmoke levels and generating a signal characteristic of said smokelevels; means for generating an alarm signal responsive to said sensingmeans detecting a predetermined smoke level; means for user testing theoperability of said smoke detector, said testing means comprising a useractuated element adapted to cause generation of said alarm signal; meansfor diminishing for a temporary time period the sensitivity of saidsmoke detector by increasing in said sensing means said predeterminedsmoke sensitivity level causing generation of said alarm signal, saiduser element being a single element and adapted to both actuate saiddiminishing means and operate said testing means; and sensitivitycontrol means for user selection of said increased predetermined smokelevel.
 18. .Iadd.A smoke detector comprising:means for sensing smokelevels and generating a signal characteristic of said smoke levels;means for generating an alarm signal responsive to said sensing meansdetecting a predetermined smoke level; and means for diminishing for atemporary time period the sensitivity of said smoke detector byincreasing in said sensing means the magnitude of said predeterminedsmoke level required for generation of said alarm signal, said smokedetector remaining reliably operative throughout substantially theentire duration of said temporary time period. .Iaddend. .Iadd.
 19. Thesmoke detector of claim 18 wherein said predetermined smoke level isabout 1.5% smoke obscuration. .Iaddend. .Iadd.20. The smoke detector ofclaim 18 wherein said increased smoke level is about 3.0% smokeobscuration. .Iaddend. .Iadd.21. The smoke detector of claim 18 whereinsaid increased smoke level is about twice said predetermined smokelevel. .Iaddend. .Iadd.22. The smoke detector of claim 18 wherein saidincreased smoke level is higher than that typically resulting fromcooking, fireplace use, excessive water vapor from bath facilities oruse of tobacco products. .Iaddend. .Iadd.23. The smoke detector of claim18 wherein said diminishing means generates a control signal toestablish said increased smoke level, said control signal beingsubstantially constant throughout generally the entire duration of saidtemporary diminished sensitivity time period. .Iaddend. .Iadd.24. Thesmoke detector of claim 18 wherein said diminishing means generates acontrol signal to establish said increased smoke level, said controlsignal being substantially constant throughout an initial portion ofsaid temporary diminished sensitivity time period. .Iaddend. .Iadd.25. Asmoke detector comprising:means for sensing smoke levels and generatinga signal characteristic of said smoke levels; means for generating analarm signal responsive to said sensing means detecting a firstpredetermined smoke level; and means for diminishing for a temporarytime period the sensitivity of said smoke detector by increasing in saidsensing means the magnitude of said smoke level required for generationof said alarm signal to a second predetermined smoke level, said secondpredetermined smoke level being a moderate smoke level which is higherthan said first predetermined smoke level whereby said smoke detectorremains reliably operative throughout substantially the entire durationof said temporary diminished sensitivity time period. .Iaddend..Iadd.26. The smoke detector of claim 25 wherein said firstpredetermined smoke level is about 1.5% smoke obscuration. .Iaddend..Iadd.27. The smoke detector of claim 25 wherein said secondpredetermined smoke level is about 3.0% smoke obscuration. .Iaddend..Iadd.28. The smoke detector of claim 25 wherein said firstpredetermined smoke level is about one-half said second predeterminedsmoke level. .Iaddend. .Iadd.29. The smoke detector of claim 25 whereinsaid first predetermined smoke level is about 1.5% smoke obscuration andsaid second predetermined smoke level is about 3.0% smoke obscuration..Iaddend. .Iadd.30. The smoke detector of claim 25 wherein said moderatesmoke level is a higher smoke level than that typically resulting fromcooking, fireplace use, excessive water vapor from bath facilities oruse of tobacco products. .Iaddend. .Iadd.31. The smoke detector of claim25 wherein said diminishing means generates a control signal toestablish said second predetermined smoke level, said control signalbeing substantially constant throughout generally the entire duration ofsaid temporary diminished sensitivity time period. .Iaddend. .Iadd.32.The smoke detector of claim 25 wherein said diminishing means generatesa control signal to establish said second predetermined smoke level,said control signal being substantially constant throughout an initialportion of said temporary diminished sensitivity time period. .Iaddend..Iadd.33. The smoke detector of claim 32 further including means foruser testing the operability of said smoke detector, both said usertesting means and said diminishing means being operable by a single useractuated element. .Iaddend. .Iadd.34. A smoke detector comprising:meansfor sensing smoke levels and generating a signal characteristic of saidsmoke levels; means for generating an alarm signal responsive to saidsensing means detecting a first predetermined smoke level; means fordiminishing for a temporary time period the sensitivity of said smokedetector by increasing the magnitude of said smoke level required forgeneration of said alarm signal from said first predetermined smokelevel to a second predetermined smoke level that is higher than saidfirst predetermined smoke level; and means for user testing theoperability of said smoke detector, said user testing means beingoperative throughout substantially the entire duration of said timeperiod while said diminishing means is operative. .Iaddend. .Iadd.35.The smoke detector of claim 34 wherein said second predetermined smokelevel is a moderate smoke level higher than that typically resultingfrom cooking, fireplace use, excessive water vapor from bath facilitiesor use of tobacco products. .Iaddend. .Iadd.36. The smoke detector ofclaim 34 wherein both said diminishing means and said user testing meansare operable by a single user actuated element. .Iaddend. .Iadd.37. Thesmoke detector of claim 34 wherein the sensitivity of said smokedetector remains reliable throughout substantially the entire durationof said diminished sensitivity time period. .Iaddend. .Iadd.38. Thesmoke detector of claim 34 wherein said diminishing means generates acontrol signal, said control signal having a substantially constantmagnitude throughout the entire duration of said diminished sensitivitytime period, whereby, responsive to said control signal, the sensitivityof said smoke detector remains substantially constant during saiddiminished sensitivity time period. .Iaddend.